{
  "id": "wheel-offset",
  "version": "2d90860d804d",
  "status": "published",
  "name": "Wheel Offset Calculator",
  "question": "How will a new wheel offset fit?",
  "summary": "Compares a new wheel with the old one from their widths and offsets: how far the inside edge moves toward the suspension and the outside edge toward the fender, and the change in track width.",
  "category": "everyday-life",
  "subcategory": "travel-and-fuel",
  "url": "https://www.acalculator.org/everyday-life/wheel-offset-calculator",
  "markdown": "https://www.acalculator.org/everyday-life/wheel-offset-calculator.md",
  "kind": "function",
  "method": "outside change = (new width − current width) ÷ 2 − (new offset − current offset); inside change = (new width − current width) ÷ 2 + (new offset − current offset)",
  "assumptions": [
    "Widths are rim widths (the “9” in 18×9), measured the same way for both wheels, usually in inches (1 in = 25.4 mm); either field takes inches or millimeters.",
    "Offset (ET) is the distance from the wheel’s centerline to its hub mounting surface, positive toward the outside face.",
    "The tire is not included: a wider tire on the same wheel sticks out further on both sides."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "w1": {
        "title": "Current wheel width",
        "description": "The rim width of the wheel on the car now, usually in inches.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "length",
        "minimum": 0.07619999999999999,
        "maximum": 0.6095999999999999
      },
      "et1": {
        "title": "Current wheel offset",
        "description": "The offset (ET) of the wheel on the car now, usually in mm.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "length",
        "minimum": -0.15,
        "maximum": 0.15
      },
      "w2": {
        "title": "New wheel width",
        "description": "The rim width of the new wheel, usually in inches.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "length",
        "minimum": 0.07619999999999999,
        "maximum": 0.6095999999999999
      },
      "et2": {
        "title": "New wheel offset",
        "description": "The offset (ET) of the new wheel, usually in mm.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "length",
        "minimum": -0.15,
        "maximum": 0.15
      }
    }
  },
  "outputs": {
    "outward": {
      "label": "Outside edge moves out",
      "description": "How much further out, toward the fender, the new wheel’s outside edge sits; negative means it sits further in.",
      "format": "quantity",
      "unit": "mm"
    },
    "inward": {
      "label": "Inside edge moves in",
      "description": "How much further in, toward the suspension, the new wheel’s inside edge sits; negative means more room.",
      "format": "quantity",
      "unit": "mm"
    },
    "track": {
      "label": "Track width change",
      "description": "The change in the distance between the outside edges of two wheels on one axle: twice the outside change.",
      "format": "quantity",
      "unit": "mm"
    },
    "offsetChange": {
      "label": "Offset change",
      "description": "New offset − current offset.",
      "format": "quantity",
      "unit": "mm"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "w1": 0.2032,
      "et1": 0.035,
      "w2": 0.2286,
      "et2": 0.03
    },
    "outputs": {
      "outward": 0.0177,
      "inward": 0.0077,
      "track": 0.0354,
      "offsetChange": -0.005
    },
    "text": "The new wheel’s outside edge moves out by 17.7 mm and its inside edge moves in by 7.7 mm."
  },
  "examples": [
    {
      "given": {
        "w1": 0.2032,
        "et1": 0.035,
        "w2": 0.2286,
        "et2": 0.03
      },
      "expect": {
        "outward": 0.0177,
        "inward": 0.0077,
        "track": 0.0354,
        "offsetChange": -0.005
      },
      "source": "Tire Rack, What Is Wheel Offset? (offset = distance from the hub mounting surface to the wheel’s centerline; https://www.tirerack.com/upgrade-garage/what-is-wheel-offset); hand calculation in content.mdx"
    },
    {
      "given": {
        "w1": 0.17779999999999999,
        "et1": 0.045,
        "w2": 0.17779999999999999,
        "et2": 0.02
      },
      "expect": {
        "outward": 0.025,
        "inward": -0.025,
        "track": 0.05
      },
      "source": "hand calculation in content.mdx"
    },
    {
      "given": {
        "w1": 0.21589999999999998,
        "et1": 0.04,
        "w2": 0.2413,
        "et2": 0.05
      },
      "expect": {
        "outward": 0.0027,
        "inward": 0.0227,
        "track": 0.0054,
        "offsetChange": 0.01
      },
      "source": "hand calculation in content.mdx: half an inch is 12.7 mm (NIST SP 811 (2008), Appendix B: 1 in = 25.4 mm)"
    }
  ],
  "sources": [
    "Tire Rack, What Is Wheel Offset?: offset is the distance from the hub mounting surface to the wheel’s centerline; positive offset tucks the wheel in. https://www.tirerack.com/upgrade-garage/what-is-wheel-offset",
    "NIST SP 811 (2008), Appendix B: 1 inch = 25.4 mm exactly."
  ],
  "related": [
    "tire-size"
  ],
  "changelog": []
}